369 research outputs found
Observations of comet Levy 1990c in the (OI) 6300-A line with an imaging Fabry-Perot
We have observed the comet Levy 1990c during 16-25 August 1990 using the MPAE focal reducer system based Fabry-Perot etalon coupled with the 1 meter telescope of the Observatory of Hoher List. The free spectral range and resolution limit of the interferometer was approximately 2.18 A and approximately 0.171 A respectively. Classical Fabry-Perot fringes were recorded on a CCD in the cometary (OI) 6300 A line. They are well resolved from telluric air glow and cometary NH2 emission. Our observations indicate that the (OI) is distributed asymmetrically with respect to the center of the comet. In this paper we report the spatial distribution of (OI) emission and its line width in the coma of comet Levy
First images of a possible CO(+)-tail of comet P/Schwassmann-Wachmann 1 observed against the dust coma background
Comet P/Schwassmann-Wachmann 1 was observed with the 2m-Ritchey-Cretien Telescope of the Bulgarian National Observatory, Rozhen, Bulgaria, using the CCD-camera and focal reducer of the Max-Planck-Institute for Aeronomy. Images were taken in a red continuum window and in the 2-0 A(exp 2)Pi - X(exp 2)Sigma(+) band of CO(+) located in the blue part of the spectrum. The red images reveal an extended dust coma. From a comparison of the red and blue images a dust reddening of 13.2 percent per 1000 A is derived. At 642 nm the magnitude of the comet with a square diaphragm of 4.5 arcsec is 16.6. The blue images, taken in the CO(+) band, show a significantly different brightness distribution which is interpreted as presence of a CO(+) coma and tail superimposed on the continuum. A column density of several 10(exp 10) CO(+) molecules cm(exp -2) is derived. The tail thickness of 10(exp 5) km is unexpectedly small. We estimate the CO(+) production rate to about 6 x 10(exp 26) CO(+) particles s(exp -1). This value does not support the idea that the outbursts of this comet are caused by crystallization of amorphous water ice
Doppler velocities in the ion tail of comet Levy 1990c
We have obtained time alternating sequences of column density maps and Doppler velocity fields in the plasma tail of comet Levy 1990c. We describe the observing technique and data analysis, and we present first results
D7-Brane Moduli vs. F-Theory Cycles in Elliptically Fibred Threefolds
We study the space of geometric and open string moduli of type IIB
compactifications from the perspective of complex structure deformations of
F-theory. In order to find a correspondence, we work in the weak coupling limit
and for simplicity focus on compactifications to 6 dimensions. Starting from
the topology of D7-branes and O7-planes, we construct the 3-cycles of the
F-theory threefold. We achieve complete agreement between the degrees of
freedom of the Weierstrass model and the complex structure deformations of the
elliptic Calabi-Yau. All relevant quantities are expressed in terms of the
topology of the base space, allowing us to formulate our results for general
base spaces.Comment: 40 pages, 15 figures, references adde
Gravitational Instantons and Fluxes from M/F-theory on Calabi-Yau fourfolds
We compactify four-dimensional N=1 gauged supergravity theories on a circle
including fluxes for shift-symmetric scalars. Four-dimensional Taub-NUT
gravitational instantons universally correct the three-dimensional
superpotential in the absence of fluxes. In the presence of fluxes these
Taub-NUT instanton contributions are no longer gauge-invariant. Invariance can
be restored by gauge instantons on top of Taub-NUT instantons. We establish the
embedding of this scenario into M-theory. Circle fluxes and gaugings arise from
a restricted class of M-theory four-form fluxes on a resolved Calabi-Yau
fourfold. The M5-brane on the base of the elliptic fourfold dualizes into the
universal Taub-NUT instanton. In the presence of fluxes this M5-brane is
anomalous. We argue that anomaly free contributions arise from involved
M5-brane geometries dual to gauge-instantons on top of Taub-NUT instantons.
Adding a four-dimensional superpotential to the gravitational instanton
corrections leads to three-dimensional Anti-de Sitter vacua at stabilized
compactification radius. We comment on the possibility to uplift these M-theory
vacua, and to tunnel to four-dimensional F-theory vacua.Comment: 47 pages, 2 figure
Hints for Off-Shell Mirror Symmetry in type II/F-theory Compactifications
We perform a Hodge theoretic study of parameter dependent families of
D-branes on compact Calabi-Yau manifolds in type II and F-theory
compactifcations. Starting from a geometric Gauss-Manin connection for B type
branes we study the integrability and flatness conditions. The B model geometry
defines an interesting ring structure of operators. For the mirror A model this
indicates the existence of an open-string extension of the so-called A model
connection, whereas the discovered ring structure should be part of the
open-string A model quantum cohomology. We obtain predictions for genuine
Ooguri-Vafa invariants for Lagrangian branes on the quintic in P4 that pass
some non-trivial consistency checks. We discuss the lift of the brane
compactifications to F-theory on Calabi-Yau 4-folds and the effective couplings
in the effective supergravity action as determined by the N = 1 special
geometry of the open-closed deformation space.Comment: 49 pages, 1 table; v2: Appendix and references added, minor
corrections; v3: discussion in sect. 2 extended, version published in
Nucl.Phys.
Open mirror symmetry for Pfaffian Calabi-Yau 3-folds
We investigate the open mirror symmetry of certain non-complete intersection
Calabi- Yau 3-folds, so called pfaffian Calabi-Yau. We perform the prediction
of the number of disk invariants of several examples by using the direct
integration method proposed recently and the open mirror symmetry. We treat
several pfaffian Calabi-Yau 3-folds in and branes with two
discrete vacua. Some models have the two special points in its moduli space,
around both of which we can consider different A-model mirror partners. We
compute disc invariants for both cases. This study is the first application of
the open mirror symmetry to the compact non-complete intersections in toric
variety.Comment: 64 pages; v2: typos corrected, minor changes, references added; v3:
published version, minor corrections and improvement
Matrix Factorizations, D-Branes and their Deformations
We review in elementary, non-technical terms the description of topological
B-type of D-branes in terms of boundary Landau-Ginzburg theory, as well as some
applications.Comment: 20p, 5 figs, Proceedings of Cargese school on string theory, 200
The effective action of D6-branes in N=1 type IIA orientifolds
We use a Kaluza-Klein reduction to compute the low-energy effective action
for the massless modes of a spacetime-filling D6-brane wrapped on a special
Lagrangian 3-cycle of a type IIA Calabi-Yau orientifold. The modifications to
the characteristic data of the N=1 bulk orientifold theory in the presence of a
D6-brane are analysed by studying the underlying Type IIA supergravity coupled
to the brane worldvolume in the democratic formulation and performing a
detailed dualisation procedure. The N=1 chiral coordinates are found to be in
agreement with expectations from mirror symmetry. We work out the Kahler
potential for the chiral superfields as well as the gauge kinetic functions for
the bulk and the brane gauge multiplets including the kinetic mixing between
the two. The scalar potential resulting from the dualisation procedure can be
formally interpreted in terms of a superpotential. Finally, the gauging of the
Peccei-Quinn shift symmetries of the complex structure multiplets reproduces
the D-term potential enforcing the calibration condition for special Lagrangian
3-cycles.Comment: 48 pages, v2: typos corrected, references adde
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